1. Field of the Invention
The present disclosure relates generally to mesostructured materials and methods of preparing mesostructured materials. More specifically, the present disclosure relates to multiply-functionalized mesostructured films and methods of preparing multiply-functionalized mesostructured films.
2. Description of Related Art
Functionalization of porous inorganic solids can be used to produce materials with novel properties that derive from their heterogeneous structures and diverse compositions. Different functionalities can be combined to introduce properties that can be additive or have synergistic local effects. In heterogeneous catalysis, this has a long history, as exploited for example in metal/acid, bimetallic, and more recently tandem catalyst systems, which typically have been in the form of powders, e.g., zeolite molecular sieves, amorphous or crystalline metal oxides or mesoporous solids. Recently, processing opportunities presented by block-copolymer-directed mesostructured solids have led to materials in film, fiber, and monolith morphologies that have been functionalized with multiple species to obtain different property combinations. In many syntheses, emphases have been placed on so-called “one-pot” protocols in which multiple components, including functional species, are incorporated simultaneously during self-assembly and formation of the inorganic network. These, however, rely on the collective compatibilities of the various components under the synthesis conditions used, which often limits the extent and diversity of the functionalities that can be introduced.
Organic functionalization of mesoporous inorganic materials in particular has attracted considerable attention, due to the attractiveness of combining a wide range of organic compound properties with the robust thermal and mechanical stabilities of high surface area inorganic solids. The anchoring of organic moieties to mesoporous inorganic surfaces by covalent bonds has generally followed two protocols, either by co-condensation of the functional species as the inorganic framework cross-links or by post-synthetic grafting of the species to accessible pore surfaces after the framework has been formed. Siliceous frameworks have been frequently prepared, due to the versatility of silica sol-gel chemistry, compatibility of soluble precursors with block-copolymer self-assembly agents, and suitability of condensed networks for post-synthesis grafting or modification. In the case of silica, co-condensation involves the simultaneous cross-linking of hydrolyzed tetraalkoxysilanes ((RO)4Si) with hydrolyzed trialkoxyorganosilanes ((RO)3SiR′, where R′ is an organic moiety), which in the presence of a structure-directing surfactant agent, yields mesostructured organically-modified silica. While co-condensation leads to the incorporation of the functional species in a single process step, removal of the surfactant species is usually required to produce the porosity needed to allow access to the functional sites in the mesopore channels. High concentrations of the precursor species tend to disrupt mesostructural ordering and make it difficult to control particle or other bulk (e.g., film, fiber, or monolith) morphologies. Additional challenges arise as the synthesis mixtures become more complicated, for example when additional co-solvent or functional species are present, due to the often competing or incompatible conditions required for their co-assembly.
In contrast, post-synthesis grafting methods are based primarily on the reactions of organosilanes ((R′O)3SiR) or halosilanes (e.g., Cl3SiR) with silanol groups on the interior mesopore channels of separately prepared (e.g., self-assembled and then calcined or solvent-extracted) mesoporous silica. This functionalization approach allows for a wide range of organic species to be anchored to silica surfaces without significantly affecting the mesostructural ordering of the silica support. Furthermore, the versatile processability of mesostructured block-copolymer-directed silica permits facile control over particle, film, fiber, or monolith morphologies and separate surface incorporation of multiple functional species, as will be shown below.
Accordingly, there is a need for a system and method for preparing mesostructured materials that have multiple functionalized locations within the structure that is easily constructed, inexpensive to produce, and has predictable functionality. The present constructs and methods satisfy these needs, as well as others, and are generally an improvement over the art.